This application relates to an indoor central heating, ventilation, and air conditioning (HVAC) system wherein control of an indoor temperature level, an indoor relative humidity level, and an indoor fresh air level are combined into one single integrated central control that is operable to manage an indoor environment during both a heating season and a cooling season.
HVAC systems are employed to control the indoor environmental characteristics of a building structure to make it comfortable for its inhabitants. A typical HVAC system includes a temperature control device or thermostat and one or more humidity control devices known as humidistats.
A thermostat is employed as a control device to regulate the indoor temperature level. Thermostats sense an actual indoor temperature and allow a user to input a desired indoor temperature. When the indoor temperature deviates from the desired level, the thermostat operates to selectively activate and deactivate a heating unit and/or an air conditioning unit and their associated blower to achieve the user desired setting.
In addition to temperature control, in order to provide a comfortable indoor environment, regulation of the indoor relative humidity of a building is also often provided. Relative humidity is defined as the ratio of the actual amount of moisture in the air to the maximum moisture capacity at a given air temperature. It is known that as temperature increases, the capacity of the air to hold moisture in the form of water vapor also increases. Conversely, as temperature decreases, the capacity of the air to hold moisture decreases and any excess moisture condenses as water on surfaces in contact with the air.
Therefore, during the winter months, the cold outdoor air has a relatively low moisture content, however, the air inside building structures is typically heated. Depending on the construction quality of a particular building, some of the cold dry outside air infiltrates into the warm indoor space and is subsequently heated to the indoor temperature. This phenomenon effectively reduces the indoor relative humidity and the indoor air becomes very dry.
To address this winter dryness or low indoor relative humidity, humidifiers are often employed as part of the central heating system. Humidifiers introduce moisture into the heated air increasing indoor relative humidity and are typically controlled by a second control device known as a humidistat. Humidistats sense an actual indoor relative humidity and allow a user to set a desired indoor relative humidity level. When the indoor relative humidity falls below the desired level the humidistat activates the humidifier to add moisture to the air. Once the desired indoor relative humidity is achieved, the humidistat deactivates the humidifier.
Conversely, to address the concern of high indoor relative humidity, devices known as ventilators are often employed. Once the indoor relative humidity exceeds the desired level the ventilator is activated to bring a controlled amount of outside dry air into the building envelope to decrease the indoor relative humidity. In addition, ventilators are also employed to bring in controlled amounts of fresh outside air to improve indoor air quality. Ventilators are typically controlled by a humidistat. However, the humidistat that controls the ventilator is typically separate from and in addition to the humidistat that controls the humidifier.
While it is known to combine temperature control and humidifier control into a single control, e.g. a thermidistat, the incorporation of a ventilator typically requires the addition of a second separate humidistat control. As such, providing year round control over all of the indoor environmental characteristics of a building structure requires the user to interface with at least two control devices to control different functions of the same HVAC system. This can be confusing for the user. Furthermore, requiring multiple control devices to control functions of the same HVAC system may at times produce conflicting results causing the system to operate at a less than optimum performance level.
In sum, to date controlling indoor environmental characteristics, such as: indoor temperature, indoor relative humidity, and indoor fresh air levels, has required the use of multiple control devices which is undesirable. As such, it is desirable to have a HVAC system which integrates control of temperature, humidity and ventilation into one single integrated central control.